There is not much Precambrian strata preserved and very few species. At this particular time, the earth, and the creatures in it, were still evolving and fossils were difficult to trace and record. There was also a noted mass extinction that occurred. Also, many Precambrian rocks have been heavily metamorphosed<span>, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata</span>
The Precambrian era is the earliest part of Earth's history. During the early Precambrian era, there were only single celled, and microscopic organisms which were virtually impossible to preserve. Later on sea life evolved into other organisms, such as jelly fish, sea cucumbers, and snails, but they are all soft tissue animals leaving behind no skeletons. Whatever shells, or fossils MIGHT have been left behind metamorphosed into other things.
